1. Field of the Invention
The present invention relates to a steering force controller for controlling a steering force generated by a power steering device by the utilization of a control circuit such as, for example, a microcomputer.
2. Description of the Prior Art
It has been known heretofore to change the steering force or the output torque relative to the input torque, of a power steering device based upon various parameters such as vehicle speed, steering rotary angle, lateral acceleration and so forth. In a known steering force controller for a power steering device, vehicle speed, steering rotary angle, lateral acceleration and so forth are detected by respective sensors, whose outputs are then processed to calculate a control electric current. This control electric current is applied to a linear solenoid valve for controlling steering force, whereby a part of pressurized fluid is controllably bypassed from a high pressure passage directly to a low pressure passage so as to change the volume of pressurized fluid to be supplied into the power steering device.
However, in the known steering force controller, no output torque is detected, resulting in the fact that the output torque cannot be controlled relative to the input torque to follow an objective characteristic even when electric current suitable to cause the output torque to follow the objective characteristic is applied to the solenoid valve. Particularly, once a disturbance causes the output torque to deviate from the objective characteristic, such deviation cannot be obviated, and therefore, the control system is unstable.